Arc blow is the deflection of a welding arc from its normal path due to magnetic forces. This condition is usually encountered in direct current welding of magnetic materials, such as iron, nickel, and their alloys. Arc blow mostly in DC welding, but can happen in alternating current welding under certain conditions, but these cases can be rare and the intensity of the arc blow is less severe. Direct current flowing through the electrode and base metal sets up a magnetic field around the electrode. The magnetic field tends to deflect the arc to the side at times, but the arc can deflect forward or backwards along the joint.
Back blow is encountered when welding toward the work cable connection on a workpiece near the end of a joint or into a corner or an edge. Forward blow is encountered when welding away from the work cable connection on a workpiece at the start of a joint. In general, arc blow can be the result of two conditions: change of current flow direction as it enters the work and is conducted toward the work cable; and asymmetric arrangement of magnetic material around the arc, a condition that can exist when welding is performed near the end of ferromagnetic materials or the workpiece and/or weld fixture has residual magnetism. Improper grounding of the workpiece can also cause arc blow.
Although arc blow cannot always be completely eliminated, what is needed is way in which to control or reduce arc blow to an acceptable level.
High current is needed to provide the melt off of the wire at high deposition. However, one problem of high current gas metal arc welding is arc instability from rotational spray arc metal transfer. To support higher current, the anode area increases such the arc climbs above the molten metal, plasticizes the wire near the molten metal and forms it into a tapered shape. The asymmetric electromagnetic Lorenz/radial pinch forces and Euler/azimuthal forces move the liquid away from its straight line of flow, and forms an unstable or unpredictable rotating liquid string tethered to the wire end with arc pressure and resulting in spiral filament motion, excessive spatter, lack of penetration, and process instability.
Further, high current for high deposition gas metal arc welding with certain shielding gas composition can suffer from finger shaped penetration due to certain energy density distribution of the arc from a round wire, heat sinking condition of the workpiece and thermodynamics of the weld puddle. The penetration profile can cause the root of the joint to be missed due to arc blow or make the part fit-up in a situation in which wire placement alignment with respect to the joint is critical. This can increase the tooling cost and part dimensional control cost to improve fit-up for a fabricator. Further, joint preparation cost (e.g., necessitating precision laser or waterjet cutting and CNC machining of the joint prior to welding) can also increase. Ultimately, weld quality can be compromised if the pre-welding operations are not controlled.
In addition, shielding gas flow may not be uniform due to turbulence, clogged gas nozzle, improper gas flow rate, out-of-position welding, and/or wind or fume exhaust that steer ionized gas plasma astray from the center of weld tool axis.
What is needed is an apparatus, system or method that keeps the arc centered and prevents the arc from straying or being disturbed for enhanced arc control, increased weld quality, and a more stable weld process.